Sibling cannibalism among juvenile vundu under controlled conditions. II. Effect of body weight and environmental variables on the periodicity and intensity of type II cannibalism

Cannibalism among starved groups of juvenile (19–48 days old) vundu catfish Heterobranchus longifilis was 66·5% nocturnal, and its impact under modified day length was proportional to the duration of the dark phase. Shallow depth and high population density decreased the intensity of cannibalism, whereas low density and deeper environments had an opposite effect. The presence of refuges had no significant effect on cannibalism. The maintenance ( R _maint) and maximum ( R _max) daily food rations (% day⁻¹) of cannibals feeding on live prey were modelled as R _maint=3·899 W _C^0·327 ( r ²=0·684; d.f.=31), and R _max=49.545 W _C^0·321 ( r ²=0·999; d.f.=5), where W _C was the body weight of the cannibal (g). The latter model indicated that the impact of a cannibal on a population decreased by a 20% margin each time the cannibal doubled its body weight, and suggested that cannibalism among vundu would become insignificant for cannibals heavier than 30 g. The significance of these findings is discussed within the contexts of vundu aquaculture and of general, conceptual models of the dynamics of cannibalism among fishes.     

Human motoneuron firing behavior and single motor unit F-wave

In motor control studies, the F-wave (a recurrent discharge evoked by an axonal antidromic volley) widely used for obtaining information on motoneuron pool behavior. However, such F-wave using is a matter of discussion and still has been not validated experimentally. The aim of the present study was investigation of F-wave properties of single firing motor units (MUs) in healthy humans, the properties, which could give evidence for F-wave origin in motoneuron soma and, therefore, could be used for estimation of a relation between MU firing and motoneuron firing behavior. In total, 91 MUs in five muscles of six healthy subjects, during gentle voluntary contractions, were studied. Peri-stimulus time histograms of single MUs were plotted. None of them revealed statistically significant increasing in MU firing probability at the F-wave latency. Analysis of relationships between characteristics of motoneuron firing behavior (mean firing frequency and target interspike interval duration) and properties of F-waves showed their independence. At the same time, it was found that F-waves were recorded in MUs, whose axons possessed the marked supernormal period in excitability recovery cycle after a discharge. Thus, the present results are in contrast to that which should be expected if the F-wave originated in the motoneuronal soma and could provide evidence for motoneuron firing behavior.     

The effects of Ramadan intermittent fasting on the underlying mechanisms of force production capacity during maximal isometric voluntary contraction

The aim of the present study was to investigate the effects of Ramadan intermittent fasting (RIF) on the underlying mechanisms of force production capacity during maximal voluntary isometric contraction (MVIC) using the superimposed twitch technique. Ten healthy male physical education students performed three MVIC of the knee extensor superimposed with nerve electrical stimulation during four testing phases: one week before Ramadan (BR), at the end of the first week of Ramadan (R-1), during the fourth week of Ramadan (R-4) and two weeks after Ramadan (AR). This study was performed during Ramadan 2016. MVIC values, voluntary activation level (VAL), potentiated resting twitch and electromyography signals were recorded during each MVIC. The French version of the Profile of Mood States questionnaire (POMS-f) was used to evaluate the subjective mood states in each testing session. The results showed that MVIC values (890.57 ± 67.90 vs. 816.46 ± 54.72 N) and VAL (87.73 ± 3.27 vs. 77.32 ± 7.87%) decreased at R-1 compared to BR (p < 0.001). However, the neuromuscular efficiency and the potentiated resting twitch remained unchanged during Ramadan (R). Results showed that depression (p < 0.01; 6.3 ± 1.57 vs. 4.7 ± 1.25), fatigue (p < 0.001; 9.2 ± 1.93 vs. 4.6 ± 2.01) and anxiety (p < 0.001; 6.4 ± 1.51 vs. 11.8 ± 1.23) scores of POMS-f were higher during R-1 compared to BR. In conclusion, RIF-related impairment of maximal muscle force seems to be related to nervous alterations of the VAL, whereas the RIF did not adversely affect peripheral mechanisms.

Abbreviations’ List: ANOVA: Analysis of variance; AR: After Ramadan; BMI: Body-mass index; BR: Before Ramadan; EMG: Electromyography; ER: End of Ramadan; MF: Mean frequency; M_max: Peak-to-peak M-wave amplitudes; MVIV: Maximal voluntary isometric contraction; NES: Nerve electrical stimulation; NME: Neuromuscular efficiency; POMS-f: French version of the Profile of Mood States questionnaire; R: Ramadan; R-1: First week of Ramadan; R-4: Fourth week of Ramadan; RF: Rectus femoris; RIF: Ramadan intermittent fasting; RMS: Root mean square; VAL: Voluntary activation level; VL: Vastus lateralis; VM: Vastus medialis.     

Mature hematology in neonatal walruses supports diving alongside their mothers

An animal's physiology limits the environmental conditions where it can persist; quantifying the physiology of the walrus is timely since they are being impacted by alterations in sea ice. We examined postnatal changes in hematology, an important attribute that supports diving, by analyzing a longitudinal data set from aquaria walruses (five males and nine females) sampled from 0.04 to 12.0 years of age (n = 795 samples). Red blood cell count (RBC), hemoglobin (Hb), hematocrit (Hct), mean corpuscular volume (MCV), mean cell hemoglobin (MCH), and mean corpuscular hemoglobin content (MCHC) did not change markedly after birth and appears to have not been influenced by sex. Estimated values at birth were RBC: 3.78 ± 0.12 × 10⁶ mm⁻³, Hb: 17.62 ± 0.82 g dl⁻¹, Hct: 45.21 ± 2.01%, MCV: 118.99 ± 3.99 fl, MCH: 47.10 ± 1.77 pg, and MCHC: 39.60 ± 0.70 g dl⁻¹. Compared to newborns, there were only subtle decreases in RBC, Hb, and MCHC, and a slight increase in MCV in the years following birth; Hct and MCH appear not to have changed. Unlike other pinnipeds, walruses swim within days of birth and have a prolonged 2-year nursing interval. Mature hematology early in life supports breath-holding, as young walruses must transit under sea ice with patchily distributed breathing holes.     

Cardiovascular shunting in vertebrates: a practical integration of competing hypotheses

This review explores the long‐standing question: ‘Why do cardiovascular shunts occur?’ An historical perspective is provided on previous research into cardiac shunts in vertebrates that continues to shape current views. Cardiac shunts and when they occur is then described for vertebrates. Nearly 20 different functional reasons have been proposed as specific causes of shunts, ranging from energy conservation to improved gas exchange, and including a plethora of functions related to thermoregulation, digestion and haemodynamics. It has even been suggested that shunts are merely an evolutionary or developmental relic. Having considered the various hypotheses involving cardiovascular shunting in vertebrates, this review then takes a non‐traditional approach. Rather than attempting to identify the single ‘correct’ reason for the occurrence of shunts, we advance a more holistic, integrative approach that embraces multiple, non‐exclusive suites of proposed causes for shunts, and indicates how these varied functions might at least co‐exist, if not actually support each other as shunts serve multiple, concurrent physiological functions. It is argued that deposing the ‘monolithic’ view of shunting leads to a more nuanced view of vertebrate cardiovascular systems. This review concludes by suggesting new paradigms for testing the function(s) of shunts, including experimentally placing organ systems into conflict in terms of their perfusion needs, reducing sources of variation in physiological experiments, measuring possible compensatory responses to shunt ablation, moving experiments from the laboratory to the field, and using cladistics‐related approaches in the choice of experimental animals.     

Seeking the sun in deep,dark places: mesopelagic sightings of ocean sunfishes (Molidae)

Evidence is presented from publicly available remotely operated vehicle (ROV) footage that suggests deep‐water ranging in ocean sunfishes (family Molidae) is more common than typically thought, including a new maximum depth recorded for the southern sunfish Mola ramsayi.     

The dangers of euthanasia and dementia: how Kantian thinking might be used to support non-voluntary euthanasia in cases of extreme dementia

Some writers have argued that a Kantian approach to ethics can be used to justify suicide in cases of extreme dementia, where a patient lacks the rationality required of Kantian moral agents. I worry that this line of thinking may lead to the more extreme claim that euthanasia is a proper Kantian response to severe dementia (and similar afflictions). Such morally treacherous thinking seems to be directly implied by the arguments that lead Dennis Cooley and similar writers to claim that Kant might support suicide. If rationality is the only factor in valuing a human life, then the loss of that rationality (however such loss might be defined) would allow us to use essentially utilitarian thinking in order to support non-voluntary euthanasia, since the patients themselves would no longer be moral agents that demand respect.     

Genetic variations and physical activity as determinants of limb bone morphology: an experimental approach using a mouse model

To gain insight into past human physical activity, anthropologists often infer functional loading history from the morphology of limb bone remains. It is assumed that, during life, loading had a positive, dose-dependent effect on bone structure that can be identified despite other effects. Here, we investigate the effects of genetic background and functional loading on limb bones using mice from an artificial selection experiment for high levels of voluntary wheel running. Growing males from four replicate high runner (HR) lines and four replicate nonselected control (C) lines were either allowed or denied wheel access for 2 months. Using μCT, femoral morphology was assessed at two cortical sites (mid-diaphysis, distal metaphysis) and one trabecular site (distal metaphysis). We found that genetic differences between the linetypes (HR vs. C), between the replicate lines within linetype, and between individuals with and without the so-called "mini-muscle" phenotype (caused by a Mendelian recessive gene that halves limb muscle mass) gave rise to significant variation in nearly all morphological indices examined. Wheel access also influenced femoral morphology, although the functional response did not generally result in enhanced structure. Exercise caused moderate periosteal enlargement, but relatively greater endocortical expansion, resulting in significantly thinner cortices and reduced bone area in the metaphysis. The magnitude of the response was independent of distance run. Mid-diaphyseal bone area and area moments, and trabecular morphology, were unaffected by exercise. These results underscore the strong influence of genetics on bone structure and the complexity by which mechanical stimuli may cause alterations in it.     

APPARENT LATERALIZED BEHAVIOR IN GRAY WHALES FEEDING OFF THE CENTRAL BRITISH COLUMBIA COAST

A digital acoustic recording tag was used to examine the 3‐D orientation of gray whales feeding along the central British Columbia coast. A total of 96 feeding dives were recorded from six different whales. More than half (53.1%) of the whales' bottom time was spent rolled at an angle greater than 45°. Whales rolled an average of 2.9 times per feeding dive, and rolling behavior was often accompanied by a negative pitch angle. Out of 282 recorded rolls, 274 (97.2%) were to the right. Likewise, 98.5% of the total time spent rolled at an angle greater than 45° was spent rolled to the right. The gray whales in this study showed a significant right‐side bias on both an individual (P≤ 0.009) and group level (P < 0.001). Based on the findings of this study and previous reports of uneven baleen wear ( Kasuya and Rice 1970 ), it is proposed that gray whales exhibit a population‐wide right‐side rolling bias similar in character to the 90/10 split of right handedness in humans.     

TWO APPROACHES TO COMPRESSING AND INTERPRETING TIME-DEPTH INFORMATION AS AS COLLECTED BY TIME-DEPTH RECORDERS AND SATELLITE-LINKED DATA RECORDERS

Time-depth recorders sample information about the three- dimensional behavior of diving animals over time and reduce this into just two dimensions, depth and time. Even so, interpretation of the data may still be difficult because of the volume of data and the detail that remains. Comparison of dive "shape" across individuals, geographical locations, or species presents problems because its analysis may involve subjective judgments or arbitrary distinctions. More constraints may be imposed if a telemetry system is used to transmit the data. Here we present two approaches for dive data compression and analysis. The first (applied before storage and transmission) selects the most important time-depth points in a profile where depth Vs. time trajectories change most significantly. The second (used to either preprocess or postprocess dive information) creates a dimensionless, depth, and duration independent index (TAD), which encapsulates the relevant information from dive profiles on where the diver centers its activity with respect to depth during a dive. Its use facilitates comparison across dives performed at different times or places, within or between individuals or species, irrespective of the duration and depth of their dives. Both can be used to reduce the amount of information sent or stored about dive behavior and can facilitate dive analysis.